We propose to understand the dynamics and control of the exchange of oxygen across the placenta, and its transport to the fetal tissues. This includes studies of the critical amount of placental diffusion required to maintain normal levels of oxygen in fetal blood, and in turn the relation of placental diffusing capacity to placental exchange area. We also will examine the effects of maternal exercise on maternal functions such as cardiac output, oxygen consumption, and uterine blood flow, and on fetal functions such as arterial oxygen levels, and concentrations of several hormones. In addition, we will examine the factors which mediate these effects. We also will explore the long-term control of fetal blood pressure, blood volume, and blood flow to several fetal organs, particularly the brain, heart, and adrenal glands. Finally, we will examine the critical levels of hypoxia produced either by breathing low oxygen mixtures or carbon monoxide which affect fetal growth and development.